Small bone angled compression screw

ABSTRACT

The present invention relates to a device and system for surgical fixation of small bones, small bone fragments, and osteotomies and more particularly to compression screw having a threaded leading portion which is joined to a section that is free from threads, and which includes an angle or from 12° to 25° in a plane through the longitudinal axis of the screw and a portion which is joined to a head having a configuration that is intended to provide anti-rotational stability and compression through the device.

FIELD OF THE INVENTION

The present invention relates to a device and system for surgicalfixation of small bones, small bone fragments, and osteotomies and moreparticularly to compression screw having a threaded leading portionwhich is joined to a section that is free from threads, and whichincludes an angle or arc from 12° to 25° in a plane through thelongitudinal axis of the screw and a trailing portion which is joined toa head having a configuration that is intended to provideanti-rotational stability and compression through the device.

BACKGROUND OF THE INVENTION

Patients often suffer from late stage arthritis in phalangeal joints ofthe hands and feet, and this presents a variety of challenges forattending physicians. While current treatment protocols usually provideacceptable results, there is a likelihood of straight distalinterphalangeal joint fusion which provides for sub-optimal outcomes.Research has shown that when a patient's distal interphalangeal joint isfused in a functional position, finger dexterity and grip strengthimprove over that of a patient with a straight fusion. Physicians canachieve angled fusions by using k-wire fixation, however, thisimmobilization protocol can fail, and lead to several complications andvaried results. While the utilization of compression screws can providereliable, strong repairs, it does not offer the additional benefit offunction flexion which is provide by a properly angled and orientedimplant fixation device, especially one, which provides the addedbenefit of compression across the joint during fusion.

Advantageous locations the use of the present invention is in thephalanges of the hand or foot. In each finger, there are three phalangesthat are separated by two joints called the interphalangeal joints (IPjoints). The proximal IP joint (PIP joint) is the one closest to the MCPjoint. The other joint closest to the end of the finger is the distal IPjoint (DIP joint). The thumb just has one IP joint. The joints arecovered on the ends with articular cartilage. The foot has an analogousstructure substituting the large toe for the thumb. It should beunderstood that there may be additional surgical techniques or locationsin the body where the device of the present invention may be suitablefor use

SUMMARY OF THE INVENTION

The present invention solves the problems associated with performing afusion technique or an osteotomy, in particular in the interphalangealjoints. The device of the invention is a compression screw having aleading portion including a beveled and/or fluted self-tapping cuttingtip, and a threaded portion, and an intermediate shaft portion whichjoins the trailing portion and forms an angle of from 12° to 25°, andpreferably 18°+/−3°. Moreover, the intermediate shaft portion is joinedto a trailing head portion that is configured to provide for compressionacross the fusion joint, and to inhibit rotation of the compressiondevice in the interphalangeal position. The head is specificallyconfigured (in a modified truncated triangular shape includinghemi-cylindrical longitudinal flange members or alternatively, a taperedconical shape having threads) to be inserted into the bone withoutdamaging the bone because it is sized and shaped to support the bonefrom the inside and to fit in the narrow confines of the intramedullarychannel of these bones, to provide a head design which providescompression across the joint, but which can be seated below the surfaceof the bone to avoid screw prominence on the digit tip or intrusion intothe fat pad of the finger or toe and the irritation that can result froma proud portion. In addition, the present invention provides for apercutaneous insertion in a surgical technique with an intramedullaryimplant designed to minimize soft tissue, cartilage and vascular damageupon insertion; and to facilitate early, active mobilizationpost-operative protocols for accelerated healing and earlier return towork.

The head at the trailing end includes a driving recess, such as ahexalobe, capable of being driven by a suitable driver into the opening.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a device in accordance with theinvention;

FIG. 2 is a side view of the device of FIG. 1;

FIG. 3 is a side view of the device of FIG. 1 taken at a rotation of 90°to the view in FIG. 2;

FIG. 4 is a cross-section of the device of FIG. 3 taken along line A-A;

FIG. 5 is a detail of FIG. 1 showing the end view of the head of thedevice from the top;

FIG. 6 is a dorsal view of a skeleton of a hand showing the implant ofthe invention in place in a PIP fusion;

FIG. 7 is an illustration of the step of inserting a guide wire in aretrograde fashion to align the distal and intermediate phalanges inaccordance with the technique of the invention;

FIG. 8 is an illustration of the step of drilling by passing acannulated drill over the guide wire;

FIG. 9 is an illustration of the step of inserting and confirming theplacement of the implant across the fusion site in accordance with thesurgical technique of the invention;

FIG. 10 is an isometric view of a second embodiment of the device inaccordance with the invention;

FIG. 11 is an end view of the device of FIG. 10 taken from a first end;and

FIG. 12 is an end view of the device of FIG. 10 taken from the secondend.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary embodiment 10 of the angled compression screwof the present invention. The screw 10 may be formed of any suitablebiocompatible material, such as surgical grade stainless steel,titanium, alloys of nickel and chromium, nitinol, PEEK, hydroxyapatite,bio-glass or other bio compatible materials or combinations of thesematerials. The screw 10 has a first end, or trailing end, 12, a secondend, or leading end, 14, a shaft 16 with an outer surface 17, and theshaft 16 including a leading portion 18 which includes a thread 19 andhas a beveled cutting tip 20 at the terminal end 22. The leading portion18 is joined to a trailing portion 24 of the shaft 16. It should benoted while that the trailing portion may be considered to be proximalto the leading portion relative to the screw itself, in use, the leadingportion is intended to be implanted more proximally in the joint thanthe trailing portion. The leading portion includes an intermediateangled area that joins the leading portion 18 of the shaft to acompression head 30 which has a driving surface 32 in a drive recess 34formed in the top of first end 12. The angle of the angled area is from10° to 25°, and preferably 18°+/−3° which is defined at the intersectionof the central longitudinal axes of the trailing portion and the leadingportions of the shaft. Accordingly, the outer surfaces of the angledportion include a slight radius. The shaft is only angled in a singleplane as can be seen in a comparison of FIG. 2 and FIG. 3.

In the first embodiment, the cutting end 20 includes a bevel and acounterbore that helps to cut through any bone left behind when the boneis drilled to receive device 10, and further provides a space to receiveextraneous material dragged along during insertion. The driving surface32 in this embodiment has a hexalobe drive configuration, although anysuitable driving configuration may be used. Other driving configurationsthat may be used include slotted, Pozidriv, Robertson, tri-wing,Torq-Set, SpannerHead, Triple Square and hex head.

In the first embodiment, the head of the compression screw 30 has aprofile as seen from the top in FIG. 5 that represents a truncatedmodified triangle. In particular, the tips of the angle of the triangleare rounded slightly and instead include hemi-cylindrical flanges 35,that serve to strengthen the head 30 in areas where the torque drivingrecess has been cut-out, and further which helps to inhibit the distalflange from rotating. The configuration is radially symmetricalgeometric shape (here a modified triangle as described below), butirregular, meaning that it is a circle of a diameter that is larger thanthe radius of the arc prescribed by the bent shaft rotated about acircle, or slightly larger than the size of the intermutually channel.Then, from 2-5 flat surfaces are designed in the circle, and optimallythree flats to carve a triangular shape, and the flats can additionallyinclude other protrusions, such as the hemi-cylindrical flanges in orderto better wedge the head into position in the intramedullary channel ofthe distal phalange to secure it in place and inhibit rotation relativeto the intermediate flange. Optionally, the terminal area of the headcan flare or widen in cross-section in order to enhance the compression.

The leading portion of the device includes a thread 19 which is definedbetween the outer diameter and the inner diameter and can suitablyinclude a right handed single start thread with a pitch of from 3-4, andpreferably at 3+/−0.5 with a similar lead value. The leading andfollowing profiles of the threads together form an angle of 60°+/−15°,and preferably 10°, and with a thread depth of 0.1 mm to 0.4 mm, andoptionally a thrust profile or buttress profile.

FIG. 6 illustrates a screw 10 in accordance with the present inventionin position across a first PIP joint to secure a fusion.

In FIG. 7, in a first step of a surgical technique in accordance withthe invention, the joint is scored for fusion and a k-wire is insertedin the intramedullary cannel in retrograde until is abuts the innerscortical surface of the phalanges,

In FIG. 8 a cannulated drill 3, uses the K-wire as a guide to drill anopening (i.e., a straight opening or hole) into the phalanges extendingthrough the fracture and providing enough space on each side of thefracture to properly position device 10.

In FIG. 9, the device 10 is driven into the opening in the phalanges bymeans of the drive recess. The outer diameter of the threads 28, isslightly larger than the inner diameter of the opening in the bone. Thisprovides bone material for threads 28 to thread into and provides atight fit for device 10. Further, the device is configured to allow abent angled screw to be screwed into a straight hole which has beenprovided in the cancellous portion of the bone and across a fusion site,but where the device includes an angle along its long axis so that therelationship of the bones, or bone segments is changed as the device isscrewed into the hole. Specifically, the device includes an angle in oneplane about its long axis which is between 10° and 25°, and morespecially which is 18°+/−3°. This angle is defined by the intersectionof the axes along the central long axis of the device, and further wherethe device includes a leading length and a trailing length eachextending from the intersection to the termination of the device (i.e.the lateral surfaces at the leading tip and the area surrounding thetorque driving recess), where the trailing length describes an arc ofrotation when it is rotated about the long axis which describes an arcof rotation diameter that is not larger than, or equal to across-sectional diameter of the head of the device below any additionaltrailing compression feature. Again, this means that the head has aconfiguration in the cross-section taken transverse to the long axiswhich is a modified regular geometric shape, such as a circle or an ovalthat has a maximum size that fill not exceed the space in the bone fromexternal cortical surface to external cortical surface, but which can be“dragged” through the bone in rotation as the threaded leading portionof the screw is screwed into the bone, but which allows the cancellousbone to fill in during healing. Thus, the head has a capability to fillthe canal of the bone that is created by the passing of the bent sectionin order to create compression in addition to having an theanti-rotation aspect which inhibits the device or the bone from rotatingfrom the intended angled orientation (so that an oddly angled phalangeis avoided while the desired fusion angle is preserved). This feature isgoverned by the largest diameter section of the head in contrast to thecuts or flats that create the anti-rotation feature.

It is noted that the head could include a trailing flared portion whichexceeds the more leading area in order to increase the feature ofcompression, and that this trailing flare has a depth along the longaxis from the trailing end of the head of less than ½, and morepreferably ¼ of the total length of the head. Thus, the head can bedragged into the bone, (which can include a counter-bored portion)without splitting the bone, and will seat below the cortical surface ofthe bone.

FIGS. 10-12 show a second embodiment of the invention which is similarto the first embodiment, except that the head is a more traditionaltapered or conical shape and is threaded in a double lead thread of thesame thread shape and pitch value or even a lower pitch value (i.e. 50%to 95%, and preferably 75% to 90% of the pitch value) as the leadingportion of the screw. The screw 110 has a first end, or trailing end,112, a second end, or leading end, 114, a shaft 116 with an outersurface 117, and the shaft 116 including a leading portion 118 whichincludes a thread 119 and has a tapered cutting tip 120, including acutting flute 121 at the terminal end 122. The leading portion 118 isjoined to a trailing portion 124 of the shaft 116 The trailing portionincludes an intermediate angled area that joins the leading portion 118of the shaft to a tapered or conical compression head 130 with a thread136 and which has a driving surface 132 in a drive recess 134 formed inthe top of first end 112.

Having thus described some embodiments of the invention, othervariations and embodiments that do not depart from the spirit of theinvention will become apparent to those skilled in the art. The scope ofthe present invention is thus not limited to any particular embodiment,but is instead set forth in the appended claims and the legalequivalents thereof. Unless expressly stated in the written descriptionor claims, the steps of any method recited in the claims may beperformed in any order capable of yielding the desired result.

What is claimed is:
 1. A compression screw for use in an angled fusionprocedure in the intramedullary channel of a bone, the screw comprising:a leading portion having a length and a central longitudinal axis, theleading portion comprising a cutting tip; a lag portion which extendsfrom the leading portion and includes a bend from the centrallongitudinal axis of the leading portion, wherein the lag portion has alength that is from ¼ to ½ of a total length of the lag and leadingportions; and a head member extending from the lag portion, the headmember comprising a torque driving recess and an anti-rotation featurethat includes a modified triangle, wherein the screw includes a singlethread extending along the leading portion and terminating prior to thebend, and wherein the bend of the lag portion defines an arc of rotationwhen the compression screw is rotated about the central longitudinalaxis, a maximum diameter of the head being larger than or equal to adiameter of the arc of rotation.
 2. A compression screw as set forth inclaim 1 wherein the modified triangle comprises a separated plurality offlats.
 3. A compression screw as set forth in claim 2 wherein the headhas three flats which are separated from one another by ahemi-cylindrical flange.
 4. A compression screw as set forth in claim 1wherein the modified triangle comprises flat surfaces that extend in thedirection of the longitudinal axis of the screw and wherein the screwhead is radially symmetrical.
 5. A method of performing a bent anglebone fusion comprising the steps of: drilling a straight hole in a firstbone or bone segment and a second bone or bone segment aided by at leasta K-wire; removing the K-wire from the straight hole; and screwing abone screw in a bent configuration in the straight hole after removingthe K-wire from the straight hole, the bone screw comprising a threadedleading portion, an intermediate portion including a bend at an anglewith a longitudinal axis of the leading portion, and a head whichextends from the intermediate portion and comprises a torque drivingfeature, wherein the bone screw is advanced into the straight hole inone direction along a longitudinal axis of the straight hole.
 6. Amethod of performing a bent angle bone fusion as set forth in claim 5wherein the head is configured to allow the leading portion and theintermediate portion prior to the bend to be screwed into the straighthole, wherein after the bone screw is screwed into the straight hole,the bone screw causes compression between the first bone or bone segmentand the second bone or bone segment.
 7. A method of performing a bentangle bone fusion as set forth in claim 6 wherein the head furthercomprises an anti-rotation feature.
 8. A method of performing a bentangle bone fusion as set forth in claim 7 wherein the anti-rotationfeature comprises a modified cylinder or a cone which further includes aplurality of flat surfaces that extend in the direction of thelongitudinal axis of the screw.
 9. A method of performing a bent anglebone fusion as set forth in claim 7 wherein the head includes externalthreads.
 10. A method of performing a bent angle bone fusion as setforth in claim 6 wherein the head includes external threads.
 11. Amethod of performing a bent angle bone fusion as set forth in claim 5wherein the head includes external threads.
 12. A compression screw foruse in an angled fusion procedure in the intramedullary channel of abone, the screw comprising: a leading portion having a length and acentral longitudinal axis, the leading portion comprising a cutting tip;a lag portion which extends from the leading portion and includes a bendfrom the central longitudinal axis of the leading portion; and a headmember extending from the lag portion, the head member comprising atorque driving recess and an anti-rotation feature that includes amodified triangle, wherein the screw includes a single thread extendingalong the leading portion and terminating prior to the bend, and whereinthe bend of the lag portion defines an arc of rotation when thecompression screw is rotated about the central longitudinal axis, amaximum diameter of the head member being larger than or equal to adiameter of the arc of rotation.
 13. A compression screw as set forth inclaim 12 wherein the modified triangle comprises a separated pluralityof flats.
 14. A compression screw as set forth in claim 13 wherein thehead has three flats which are separated from one another by ahemi-cylindrical flange.
 15. A compression screw as set forth in claim12 wherein the modified triangle comprises flat surfaces that extend inthe direction of the longitudinal axis of the screw and wherein thescrew head is radially symmetrical.